Locomotives (or other vehicles) typically include a prime mover that is powered by a fuel source to generate mechanical energy. In one example of a locomotive, mechanical energy generated by the prime mover may be converted to electrical energy that is used to power traction motors and other components and systems of the locomotive. In some examples, the prime mover may be a combustion engine that is fueled by diesel, gasoline, or other liquid petroleum distillates. In other examples the engine may additionally or alternatively utilize a gaseous fuel, such as natural gas.
In light of its favorable energy content, liquefied natural gas (LNG) may be used as a fuel source for a locomotive prime mover. Particularly for long-haul applications, it may also be desirable to utilize a fuel tender for carrying one or more LNG storage tanks. The fuel tender may be coupled to the locomotive prime mover. Prior to injection into a locomotive's natural gas-fueled engine, LNG is typically vaporized into gaseous natural gas (CNG).
In one example, a fuel level of an LNG storage tank on the fuel tender may be determined using a bubbler method wherein vaporized LNG within the fuel container is used to make CNG that is bubbled in the LNG storage tank. The fuel level is then determined based on the gas pressure of the bubbled vapor. A fuel volume may then be determined based on the fuel level and a geometry of the LNG storage tank. However, when the prime mover is moving, the fluid level in the LNG storage tank may not be consistent, thereby reducing the accuracy of the fuel level and fuel volume measurements. As a result, measuring the fuel level in this way may only be accurate when the fuel tender is stationary or has been stationary for a duration. Inaccurate fuel level and fuel volume measurements may result in degradation of LNG usage control leading to LNG supply issues.